The present invention relates to fiber optic probes for use in spectroscopic applications in general and, in particular, it concerns a hybrid. Attenuated Total Reflection (ATR) fiber optic probe device. Additionally, it concerns a method for attaching a solid optical fiber core tip to hollow fiber waveguides.
More specifically, the present invention relates to a probe device and innovative accessories used in conjunction with a detecting system such as, but not limited to, a spectrophotometer or a spectrometer. The probe device of the present invention is especially well suited for use with Fourier Transform spectrometers. The accessories utilize transmitting optical waveguides, radiation sources, opto-mechanical components (reflectors, etc.) to enable spectral analysis of samples remotely from the detector or measuring system using Attenuated Total Reflectance (ATR).
It is an object of the invention to provide a hybrid fiber optic probe for spectroscopic ATR applications that has high efficiency over a wide range of wavelengths (UV, VIS, IR). In certain embodiments it can have a small diameter and have high flexibility.
Fiber optic probes for spectroscopic applications are well known and have long been used to measure the properties of samples at different states.
In general, and especially in medical applications, such fiber optic probe comprises a first fiber or a first bundle of fibers to guide radiation from the proximal end of the probe to the distal end of the probe, and a second fiber or second bundle of fibers are used to guide radiation back to the proximal end of the probe.
An optical element such as an Attenuated Total Reflectance (ATR) head or tip is arranged at the distal end of the fiber probe. The optical element generally is arranged and adapted in a way that it interacts with a sample, such as biological tissue, for determining the spectroscopic properties (spectral signatures) of the sample. In doing so, radiation emitted by the ATR element is modified by the sample, reenters the ATR element and is reflected back into the optical fiber or the bundle of the optical fibers. The reflected light eventually is emitted from the proximal end of the fiber and can be received by a detecting system such as a spectrometer based on diffraction grating, Fourier Transform spectrometer/interferometer or spectral filter with a related photo-element or array of detectors.
The ATR crystals that are remotely linked to detecting system (e.g., FTIR spectrometers) by way of fiber optics are widely used in spectroscopic applications. Single-fiber systems (systems using one input and one output optical fiber) are commonly used and generally include complex coupling means to transfer radiation from the optical fiber into the ATR crystal and back again.
ATR spectrometry is used extensively in clinical assays, medical diagnostics, and lab testing.
Examples of such ATR fiber optic probes are disclosed in U.S. Pat. Nos. 5,754,722, 7,956,317, 6,879,741, 6,563,992, 4,930,863, 6,841,792, 5,170,056, 6,970,623, 5,185,834, 5,070,243.
The ATR technique makes use of the fact that, pursuant to Snell's Law, when the beam of light impinges on the interface between the first and second medium at or above a critical angle, defined as θcrit=sin−1n2/n1 (where n1, n2 are the refractive indexes of first and second medium respectively), there is no refracted ray, i.e., the incident light is totally internally reflected, and an evanescent wave is generated. “Evanescent” means “tending to vanish,” which is appropriate because the intensity of evanescent waves decays exponentially with distance from the interface at which they are formed. This distance is typically in the 1-50 um range. As a result the intensity of the reflected light is reduced at those wavelengths at which the surrounding medium absorbs.
In AIR spectrometry, a sample is measured by passing radiation through an optical element (crystal), which can be mounted on a probe. The radiation, which for example can be UV, Vis, or IR, is directed onto the optical element at an angle of incidence such that all incident radiation undergoes total internal reflection. When the radiation undergoes total internal reflection, an electro-magnetic radiation field (evanescent wave) extends beyond the surface of the optical element into the sample. The depth of penetration of the evanescent wave is a function of the refractive index of the optical element material, refractive index of the sample material, angle of incidence of the radiation wavefront, and wavelength of the radiation. In regions of the spectrum where the sample absorbs energy, the evanescent wave is attenuated and the attenuated energy is passed back to the optical element. The radiation then exits the optical element and impinges a detector through optical waveguide/fiber. The detector records the attenuated radiation, which can then be transformed to generate a spectrum, e.g., absorption spectra.
An ATR spectrum is generated by transmitting radiation, which can be IR (from about ˜0.75 um to ˜0.1 mm), VIS (˜0.35 um to ˜0.75), or UV (from ˜0.22 um to ˜0.35 um), through an optical crystal (element) in contact with a sample and then determining what portion of the incident radiation is attenuated by the sample at a particular wavelength.
The spectrum of the transmission losses is the basis of attenuated total reflectance (ATR) spectroscopy.
There is therefore a need for a hybrid Attenuated Total Reflection (ATR) fiber optic probe device. Additionally, there is a need for a method for attaching a solid optical fiber core tip to hollow fiber waveguides.